Molybdenum disulfide containing lubricant

ABSTRACT

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF A BASE OIL CONTAINING FROM ABOUT 0.25% TO ABOUT 30% MOLYBDENUM DISULFIDE PARTICLES LESS THAN ABOUT 3 MICRONS IN SIZE SUSPENDED THEREIN AND A DISPERSANT PRESENT IN AN AMOUNT OF FROM ABOUT 0.2 TO ABOUT 0.8 PARTS DISPERSANT PER PART MOLYBDENUM DISULFIDE PRESENT, SAID DISPERSANT CONSISTING OF A COPOLYMER OF A METHACRYLATE ESTER AND N-VINYL PYRROLIDONE F AN AVERAGE MOLECULAR WEIGHT OF ABOUT 350,000 TO ABOUT 600,000 CORRESPONDING TO THE FORMULA:   -(CH(-N&lt;(-CH2-CH2-CH2-CO))-CH2)M-(CH2-C(-CH3)(-COO-R&#39;&#39;))N-   WHEREIN R7=AN ALKYL RADICAL OF C1 TO C22; AND RATIO OF M:N=1:5 TO 1:15.

United States Patent 3,842,009 MOLYBDENUM DISULFIDE CONTAINING LUBRICANT Henry F. Barry and Calvin J. Hallada, Ann Arbor, and

Fred W. Moore, Plymouth, Mich., assignors to American Metal Climax, Inc. No Drawing. Filed Oct. 19, 1970, Ser. No. 82,166 Int. Cl. Cm 1/12, 3/26, 1/32 US. Cl. 25225 9 Claims ABSTRACT OF THE DISCLOSURE A liquid lubricant composition comprising a homogeneous stable suspension of finely-particulated molybdenum disulfide in a base oil incorporating a dispersant comprising a specific copolymer of a methacrylate ester and N-vinyl pyrrolidone which is present in controlled proportions relative to the quantity of molybdenum disulfide present. The invention also encompasses the process of forming such homogeneous stable suspensions, as well as concentrates thereof.

BACKGROUND OF THE INVENTION The plate-like laminar form of particles of various metal sulfides renders such compounds useful as lubricants and agents for enhancing the lubrication characteristics of other base lubricants. Of the various metal sulfides known, molybdenum disulfide or molybdenite is best known and most extensively used for this purpose. Particularly successful results have been obtained by employing finely-divided molybdenum disulfide particles in various grease and base oil compositions so as to effect an enhancement in the lubricating properties thereof. A continuing problem associated with such liquid lubricant compositions has been the tendency of the suspended molybdenum disulfide particles to settle out during quiescent storage over relatively short time periods. Attempts to increase the homogeneity and longevity of such suspensions have not met with significant success and, accordingly, the lack of stability of such liquid lubricant compositions and/or the high cost of their preparation, has detracted from a more widespread commercial use thereof.

The decrease in fuel consumption and the increase in engine power of conventional internal combustion engines under heavy-duty operating conditions have clearly been evidenced in tests employing motor oils containing controlled amounts of molybdenum disulfide suspended therein. While such tests clearly evidence the desirability of providing motor oils incorporating molybdenum disulfide particles therein, up until the present invention, no economically and commercially satisfactory technique was available for preparing homogeneous suspensions which were further characterized as having excellent stability over prolonged periods of quiescent storage, such as normally encountered in the distribution and sale of motor oils and additives therefor.

SUMMARY OF THE INVENTION The benefits of the present invention are based on the discovery that by employing a specific dispersant of a controlled chemical composition in controlled proportions relative to the quantity of molybdenum disulfide present, and by employing the molybdenum disulfide in a controlled particle size, stable suspensions of such molybdenum disulfide particles can be readily and economically attained, enabling its adaptation for compounding conventional motor oils to achieve improved engine performance, particularly under heavy-duty operations. Specifically, the present invention, in its composition aspects, is based on the discovery that by employing a dispersant composed of a copolymer of a methacrylate ester and N-vinyl pyrrolidone of an average molecular weight ranging from about 350,000 to about 600,000 in an amount of about 0.2 up to about 0.8 part per weight for each part by weight of molybdenum disulfide particles present, a substantially homogeneous and stable suspension is provided having a longevity of upwards of six months even during quiescent storage. conventionally, the lubricant suspension can be prepared in the form of a concentrate containing from about 5% up to about 30% by weight of molybdenum disulfide particles which can thereafter be conveniently added and/or blended with a neat motor oil so as to provide a final operating concentration usually ranging from about up to about 5% by Weight molybdenum disulfide.

In the process aspects of the present invention, the molybdenum disulfide particles are reduced to an appropriate particle size or less than about 3 microns employing a fluid energy reduction mill, whereafter the particles are dispersed in a suitable base oil employing a Cowles-type mixer in the presence of the dispersing agent, forming a homogeneous suspension of the particles in the base oil.

Additional advantages and benefits of the present invention will become apparent upon a reading of the description of preferred embodiments and the specific examples as hereinafter set forth.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The concentration and/or percentages of the various constituents in the lubricant composition as herein described and as set forth in the subjoined claims are expressed in terms of a weight basis unless specifically designated to the contrary.

The improved stability of the liquid lubricants incorporating molybdenum disulfide particles in accordance with the present invention is based on the use of a controlled amount of a particlular methacrylate ester/N-vinyl pyrrolidone copolymer in relation to the amount of molybdenum disulfide particles present. The copolymer can be represented by the following structural formula:

wherein R' =an alkyl radical of C to C and Ratio of m:n==l:5 to 1:15.

In accordance with the preferred practice of the present invention, the R constituent of the methacrylate ester is selected so as to average at least about C to provide optimum dispersibility of the molybdenum disulfide particles and solubility of the dispersant in most organic lubricating compositions. In addition to the foregoing, the

dispersant is selected so as to have an average molecular weight ranging from about 350,000 up to about 600,000 and preferably about 500,000. The ratio of mm may range from about 1:5 to about 1:15 and is preferably controlled at about 1:12.

The quantity of the dispersant employed is dictated by the quantity of molybdenum disulfide particles present. Generally, the dispersant is used in an amount of about 0.2 to about 0.8 parts per part molybdenum disulfide present and preferably from about 0.35 to about 0.45 parts dispersant per part molybdenum disulfide. The concentration of the molybdenum disulfide particles generally can range from about 0.25% up to about 30% based on the total weight of the liquid lubricating composition. In accordance with the preferred practice of the present invention, concentrates of molybdenum disulfide suspensions in a base oil incorporating the dispersant are formed so as to contain from about 5% to about 30%, and preferably from about to about 20%, molybdenum disulfide. Such concentrates can conveniently be added to the motor oil present in a crankcase so as to provide an actual operating range of about 0.25% to about 5% and preferably a diluted concentration of about 0.5% to about 3% molybdenum disulfide. The specific concentration of molybdenum disulfide particles present in the motor oil in an internal combustion engine crankcase can be varied within the aforementioned ranges depending uponthe specific conditions under which the engine is operated, as well as specific engine design characteristics as they relate to frictional loading imposed upon engine components. In most instances, molybdenum disulfide concentrations of about 0.5 to about 3% have been found to provide satisfactory performance and to provide significant improvements under high speed and/ or heavyduty operating conditions when incorporated in conventional motor oils used in present-day internal combustion engines.

The molybdenum disulfide particles suspended in the base oil are controlled so as to be of a particle size less than about 3 microns and preferably of an average particle size less than about one micron. In view of the platelet configuration of the molybdenum disulfide particles, it is perhaps more accurate to express particle size from the standpoint of total surface area of the powder which, for the purposes of the present invention, is at least about 10 square meters per gram and preferably from about square meters up to about square meters per gram. While modybdenum disulfide powders having a degree of fineness in size about 20 square meters per gram can be employed, the relatively large surface area increases the susceptibility of such molybdenum disulfide powders to oxidation attack during the comminution and blending thereof, resulting in an undesirable high acid number and oxide content. It is for this reason that molybdenum disulfide powders having a surface area ranging from about 15 to about 20 square meters per gram are preferably employed.

The base oil to which the molybdenum disulfide particles and dispersant are added for forming either a concentrate or the final diluted motor oil may comprise any known synthetic or mineral base oil suitable for use as a motor oil in internal combustion engines. Generally, such base oils preferably have a viscosity ranging from an SAE 5W up to about 50. Such base oils may additionally contain other well known lubricant additives which are compatible with the dispersant and molybdenum disulfide particles present and which do not otherwise adversely affect the stability of the molybdenum disulfide suspension.

In its aspects, the present invention encompasses the comminution of the molybdenum disulfide to a particle size within the aforementioned range employing an air micronizer in accordance with the technique as described in U.S. Pat. No. 3,082,065, granted Mar. 19, 1963, which is assigned to the same assignee as the present invention.

In accordance with the method described in the aforementioned patent, the details of which are incorporated herein by reference, a powdered mass of molybdenite concentrate, usually derived from the flotation extraction operation of molybdenite ore, which contains from about 0.25% to 8% of the flotation oils, is charged directly into a fluid energy reduction mill wherein the particles become entrained in a high velocity gas, such as air. The turbulence present in the cyclonic fiow of gas causes mutual impact to occur between the entrained particles, effecting a pulverization thereof to a reduced particle size. By virtue of the centrifugal action present in the mill, the heavier or larger particles are retained within the mill for further reduction, while the finer particles are entrained in the exhaust gas and are extracted from the mill. In addition to the foregoing, but controlling the temperature of the milling fluid, such as air or steam, for example, a controlled extraction and corresponding reduction in the oil and moisture content of the comminuted molybdenite can be effected simultaneously with the pulverization of the molybdenite to a desired particle size.

The resultant molybdenum disulfide powder derived from the fluid energy reduction mill, or as many otherwise be provided, is admixed with a suitable base oil in the desired concentration range and is suspended by subjecting the mixture to high shear agitation, such as encountered in a Cowles-type mixer. In accordance with this blending procedure, the base oil incorporating usually from about 5% up to about 30% molybdenum disulfide particles is subjected to a high shear agitation by means of a relatively flat disk supported on and rotated at high speed by means of a shaft so as to effect a separation of agglomerates of the individual molybdenum disulfide particles into single particles and a substantially uniform distribution thereof throughout the base oil.

The resultant blend or slurry is thereafter subjected to a particle size separation, which preferably is performed in a disk-type centrifuge such as Sharples centrifuge, to effect the removal of any extraneous large-size molybdenum disulfide particles or agglomerates present. In this regard, it has been found that the extraction of such oversized molybdenum disulfide particles is substantially facilitated in the absence of any dispersant in the blend.

At the completion of the particle size separation step,

an appropriate amount of dispersant is added to the centrifuged blend, which is again subjected to a high shear mixing in a Cowles-type mixer. The dispersant can conveniently be introduced in the form of a concentrate in a neutral oil, which may conveniently range from about 30% up to a 50% concentration in a light oil having a viscosity of about SAE 5. The composite blend containing the base oil, the molybdenum disulfide particles and the dispersant, along with other compatible additives, is mixed for an additional period, usually of about one hour. While mixing times in excess of about one hour can be satisfactorily employed, it has been found that no appreciable improvement in the stability of the resultant motor oil suspension is achieved and, therefore, such longer mixing periods constitute an uneconomical usage of equipment.

At the completion of the mixing cycle, the resultant blend, which is in the form of a concentrate, is removed from the mixing apparatus and can thereafter be placed in suitable containers until eventual use, at which time it is added to the crankcase of an engine. Concentrates prepared in accordance with the aforementioned process containing between about 10% to about 20% molybdenum disulfide particles have been observed to be of excellent stability when placed in quiescent storage for periods of time ranging from about 6 to about 12 months.

In order to further illustrate the improved lubricating oil composition and process comprising the present invention, the following examples are provided. It will be understood that the examples are provided for illustrative purposes and are not intended to be limiting of the scope of the invention as set forth in the subjoined claims.

Example I One hundred pounds of a technical grade molybdenum disulfide powder having an average particle size of about 3 to about 5 microns was placed in a fluid energy reduction mill in accordance with the technique as previously described with reference to U.S. Pat. No. 3,082,065. Prior to the addition of the molybdenite powder to the mill, 0.25% of a neutral mineral oil was admixed with the powder to minimize surface oxidation thereof during the milling operation. The milling was performed in a two-stage operation resulting in the recovery of substantially all of the molybdenite powder which was of an average particle size of less than about 0.5 microns and surface area greater than about 15 square meters per gram.

The resultant molybdenum disulfide powder was admixed with 300 pounds of a typical SAE-20W motor oil in a Cowles-type mixer forming a slurry containing a nominal 25% molybdenum disulfide. After blending for a period of about one hour, the resultant slurry was pumped through a disk-type Sharples centrifuge whereby substantially all of the particles above about 2 microns were extracted in the form of a sludge containing 50 pounds oil and 20 pounds molybdenite and. the resultant filtered slurry was again returned to the Cowles mixer. At this point, 32 pounds of a copolymer of a methacrylate ester and N-vinyl pyrrolidone having an average molecular weight of about 500,000 was added and uniformly blended in the slurry. The dispersant was added in the form of a liquid solution comprising a neutral mineral oil of an SAE 5 viscosity incorporating 40% by weight of the dispersant therein. After mixing for an additional one hour period, the resultant concentrate, having a nominal concentration of 19.5% molybdenum disulfide, was removed from the mixer.

The resultant concentrate was tested for stability by placing a portion thereof in quiescent storage. After a period of two months, the concentrate was found to contain in excess of about 96% of the original molybdenum disulfide particles still in suspension. Another portion of the concentrate was added to a Havoline 20-20W motor oil to provide an operating concentration of about 3% molybdenum disulfide. A second portion was similarly diluted with the same motor oil to provide a 1% molybdenum disulfide operating concentration.

The resulting motor oil was tested under engine dynamometer conditions to measure variations in brake horsepower and brake specific fuel consumption in an Oldsmobile engine over an r.p.m. range of 2100 to 4800 under wide-open throttle conditions. The motor oil containing 1% molybdenum disulfide evidenced a 3.6% increase in horsepower over the entire engine speed range with an average increase of about 3.4% over the r.p.m. range of 3300 to 4800. At the same time, a 5.6% decrease in fuel consumption was noted over the entire speed range, while a 5.5% average decrease in fuel consumption was obtained over the 3300 to 4800 r.p.m. range. Similar satisfactory results were obtained with the motor oil having about a 3% concentration in molybdenum disulfide wherein an average of 2.8% increase in horsepower was obtained over the entire speed range tested, with an average increase of about 1.9% at the 3300 to 4800 r.p.m. level. A decrease of about 5% in fuel consumption was observed over the entire speed range, while a decrease of about 4.3% was noted over the r.p.m. range of 3300 to 4800.

These data clearly evidence the performance benefits resulting from the inclusion of molybdenum disulfide particles in a finely-suspended state in motor oils in accordance with the practice of the present invention.

Example II The concentrate prepared in accordance with Example I was admixed with a Super Shell 10W-30 motor oil to similarly provide concentrations of the molybdenum disulfide constituent at levels of 1% and 3%, respectively. Dynamometer tests simulating actual road conditions confirmed the same results obtained in the tests conducted in accordance with Example I.

In addition to the engine dynamometer tests conducted, actual road testing was performed employing a 1969 Mercury car. Comparisons between vehicle performance obtained during an 8,000 mile test using a conventional base oil with the results obtained during an 8,000 mile test using the same base oil incorporating a suspension of molybdenum disulfide particles confirmed the benefits previously evidenced in the engine dynamometer tests.

While it will be apparent that the embodiments of the invention herein disclosed are well calculated to fulfill the objects stated herein, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the spirit thereof.

What is claimed is:

1. A lubricant composition consisting essentially of a base oil containingfrom about 0.25% to about 30% molybdenum disulfide particles less than about 3 microns in size suspended therein and a dispersant present in an amount of from about 0.2 to about 0.8 parts dispersant per part molybdenum disulfide present, said dispersant consisting of a copolymer of a methacrylate ester and N-vinyl pyrrolidone of an average molecular weight of about 350,000 to about 600,000 corresponding to the formula:

Ratio of m:n=1:5 to 1:15.

2. The lubricant composition as defined in claim 1, wherein said dispersant is of an average molecular weight of about 500,000.

3. The lubricant composition as defined in claim 1, wherein said dispersant is present in an amount of from about 0.35 to about 0.45 parts dispersant per part molybdenum disulfide present.

4. The lubricant composition as defined in claim 1, wherein said alkyl radical in said dispersant averages at least about C 5. The lubricant composition as defined in claim 1, wherein said molybdenum disulfide particles are of a size wherein one gram thereof has a surface area of at least about 10 square meters.

6. The lubricant fcomposition as defined in claim 1, wherein said molybdenum disulfide particles are of a size wherein one gram thereof has a surface area of about 15 to about 20 square meters.

7. The lubricant composition as defined in claim 1, comprising a crankcase motor oil in which said molybdenum disulfide particles are present in an amount of about 0.5% to about 3%.

8. The lubricant composition as defined in claim 1, wherein said base oil comprises a crankcase motor oil having a viscosity of about SAE-SW to about 50.

9. The lubricant composition as defined in claim 1, wherein the ratio of m to n of said copolymer is about 1:12.

(References on following page) a 7 .Y 7 7 References Cited I FOREIGN PATENTS UNITED STATES PATENTS 774,098 12/1967 Canada' 252-25 7/1964 Bauer 252--51.5 A 9/1964 Bauer A 5 DANIEL E. WYMAN, Pnmary Exammer 1/1965 Thomas 25251.5 A I. VAUGHN, Assistant Examiner 10/1965 Bauer 252-515 A 5/1966 Akers 252-51.5 A US. Cl. X.R. 10/1966 Cyphers et a1. 25225 9/1968 Grimm et a1. 252-515 10 2 1.5 A 4/1971 Adair et a1. 252-25 

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF A BASE OIL CONTAINING FROM ABOUT 0.25% TO ABOUT 30% MOLYBDENUM DISULFIDE PARTICLES LESS THAN ABOUT 3 MICRONS IN SIZE SUSPENDED THEREIN AND A DISPERSANT PRESENT IN AN AMOUNT OF FROM ABOUT 0.2 TO ABOUT 0.8 PARTS DISPERSANT PER PART MOLYBDENUM DISULFIDE PRESENT, SAID DISPERSANT CONSISTING OF A COPOLYMER OF A METHACRYLATE ESTER AND N-VINYL PYRROLIDONE F AN AVERAGE MOLECULAR WEIGHT OF ABOUT 350,000 TO ABOUT 600,000 CORRESPONDING TO THE FORMULA: 